The most common and most likely answer to this crossword clue is the 9 letter word QUEASIEST
Q
U
E
A
S
I
E
S
T
More clues leading to the result QUEASIEST
Buddy explains!

The straight part
We know that "most uncomfortable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most uncomfortable = queasiest.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does QUEASIEST mean?
QUEASIEST adjective- Experiencing or causing nausea or uneasiness, often characterized by an unsettled stomach.
- Easily troubled; squeamish.